No more drama: Portable, accurate, and affordable In/Out tennis line call device saves time and nerves!

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Did you know we have tennis-product inventors in Women’s Tennis Blog’s community? Grégoire Gentil is a familiar name to all those active in the comments on this website and now I’m excited to tell you that he has created a revolutionary portable device that can be attached to a net post and detect whether tennis shots are in or out, with 99% accuracy. The GoPro-sized product, that will be available this summer for $199, has a simple and telling name: “In/Out”. Besides being designed to eliminate endless arguments over line calls, the In/Out helps players learn from their mistakes through HD video and analyzes their game through stats analysis.

Frustrated by countless controversies over questionable ball marks on/near lines on the Paris claycourts where he was raised, Gregoire, who now lives in Palo Alto, has developed a tennis product whose artificial intelligence software scans the court to find the lines, supported by cameras similar to those found in smartphones, and tracks the ball’s flight, pace, and spin. The In/Out beeps and/or flashes when a shot sails long or wide, while on close calls you can watch video replay on the device’s screen. Moreover, the In/Out gives you shot analysis, including distance covered by players and their depth position calculated in real-time, and the placement analysis, featuring percentage by zones, shot height and position.

What makes the In/Out stand out from other devices in this field, namely Hawk-Eye and PlaySight, is its price, which is just a fraction compared to the competition. While Hawk-Eye and PlaySight do provide a greater depth of insight, the In/Out is the only portable and affordable option tennis players have.

Grégoire has spent the last two years to develop the In/Out and he did leverage from his previous inventions, such as a hand-size drone that can follow a person around.

Now that I’ve introduced the In/Out, let’s hear what Grégoire told Women’s Tennis Blog about the biggest challenges he faced during the product development and how he envisages its future.

Q: What was the most challenging aspect in the process of creating this device?

Both hardware and software have their own challenge.

For hardware, my main goal was the price of a tennis racquet (aka. $199). So it really limits the hardware capabilities. I would have loved to use super high-end and super expensive cameras and processor, but the affordable pricing wouldn’t have been possible.

For software, it’s really about computer vision! This is the same kind of technology you have in self-driving car. It requires a lot of tuning to adapt to all conditions.

Q: How do you see the future of the In/Out?

The plan is to target a release hopefully this summer. There will be a first batch (you can donate at to get a reserved place) and then I will see how it goes.

Hardware will be final in the summer batch, software might be in beta. Like the Tesla!

Long term, doing other ball sports (volley ball, badminton, even basketball) would really makes sense with this kind of technology.

I really hope that Grégoire’s product will be a common sight on tennis courts worldwide! For more information and product purchase, visit the In/Out website.


  1. I hope this will impact tournament play positively and keep the FAIR players on a level playing field. Will it be approved? Time will tell. The hurdles will most likely be when multiple courts are using them side by side. The audible feature would be overridden. Also what about a ball from another court or one from a players pocket or hand dropping coming onto the court.


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